The mechanism of iodide accumulation by the brown sea weed Laminaria digitata. II. Respiration and iodide uptake.

Iodide absorption by fresh, summer Lam inaria digitata frond was accompanied b y about a fivefold increase in the rate o f oxygen consumption. Betw een approxim ately 3 and 6 m ole­ cules o f Oa were consumed for each iodide ion absorbed by the tissue and the respiratory quotient, whether measured in the presence or absence o f iodide, lay between 0*9 and 1*1 (mean 0*94). I t is argued th a t: (1) The iodide-stimulated respiration m ust occur principally near the surface of the frond, though this localization is not due to the lim ited diffusibility o f oxygen. (2) Iodide absorption is connected w ith the oxidation o f a carbohydrate-like compound or compounds. (3) The absorption of iodide is associated w ith a rate-limiting process for the oxidation of the compound or compounds. (4) Betw een one and two iodide ions are absorbed for each six-carbon unit oxidized. (5) Probably only one or two reactions in the oxidation o f each six-carbon unit is involved in iodide absorption, one of these reactions being the rate lim iting process governing the oxidation.